is_same_response & get_correct_response must include validation values.

question.php

@@ -292,13 +292,16 @@ class qtype_stack_question extends question_graded_automatically {
         $teacheranswer = array();
         foreach ($this->inputs as $name => $input) {
             $teacheranswer[$name] = $input->maxima_to_raw_input($this->session->get_casstring_key($name));
+            if ($input->requires_validation()) {
+                $teacheranswer[$name . '_val'] = $teacheranswer[$name];
+            }
         }
 
         return $teacheranswer;
     }
 
     public function is_same_response(array $prevresponse, array $newresponse) {
-        foreach ($this->inputs as $name => $input) {
+        foreach ($this->get_expected_data() as $name => $notused) {
             if (!question_utils::arrays_same_at_key_missing_is_blank(
                     $prevresponse, $newresponse, $name)) {
                 return false;